Imagine walking through a neighbourhood and seeing graffiti, litter, and shopping trolleys strewn about the place. Are these problems to be solved, or petty annoyances that can be ignored in the light of more serious offences? A new study suggests that the former is right – even the most trivial of transgressions can spread and spiral because their very presence stimulates more of the same behaviour. Through a series of stunning real-world experiments, Kees Keizer and colleagues from the University of Groningen have shown that disorder breeds more disorder. The mere presence of graffiti, for example, can double the number of people who litter and steal.

Their study provides strong support for the controversial Broken Windows Theory, which suggests that signs of petty crimes, like broken windows, serve as a trigger for yet more criminal behaviour. It follows that fixing small problems can prevent the build-up of bigger ones and the gradual decay of a neighbourhood. The idea was first proposed in a magazine article published in 1982, but soon became the basis of many a social policy.

It inspired Rudy Guiliani’s Quality of Life Campaign in New York, which focused attention on seemingly trivial fixes such as removing graffiti, clearing signs of vandalism and sweeping the streets. The campaign seemed to work, which motivated other cities to try the same tactics. But despite its popularity, the Broken Windows Theory still divides opinion, for it lacks the backing of hard evidence, it’s plagued by woolly definitions of “disorder” and critics have questioned its role in New York’s drop in crime. These are fairly hefty shortcomings for a concept that is so central to anti-crime measures and Keiser wanted to address them once and for all.

To do so, he took to the streets of Groningen and watched unknowing passers-by in real-life situations as they reacted to signs of disorder. The recurring question was this: would people exposed to inappropriate behaviour behave in a similar way themselves?

He began in an alleyway in a local shopping district, where bicycles are commonly parked and where a conspicuous red sign warned against graffiti. He attached a flyer from a fictional sportswear shop to the handlebars of parked bicycles and watched what people did as they returned to their rides. Under normal circumstances (picture on the left), most people took the flyer with them and just 33% littered by throwing it on the ground. But that all changed when Keiser covered the wall with graffiti (picture on the right). With this innocuous difference, the proportion of litterers doubled and 69% discarded their flyers on the street.

Keiser explains this behaviour in terms of “social norms” – the rules that separate appropriate behaviours from inappropriate ones. Problems arise when our view of what is common (in this case, graffiti) fails to mesh with our understanding of what society expects (as epitomised by the “No Graffiti” sign). Graffiti is frowned upon, but the covered walls send a message that it is common and therefore, more acceptable. Keizer calls this the Cialdini effect.

To see how far its influence would extend, he set up a temporary fence in front of a car park. He attached two signs to the fence, one banning people from locking their bicycles to it, and another saying that entry was forbidden and asking people to use a detour some distance away. When he placed four bicycles a metre away, just 27% of people disobeyed the detour sign and squeezed through the gap in the fence. But when the bikes were locked to the fence, in blatant disregard of the first sign, 82% of people ignored the detour sign too. With one rule broken, the other followed suit.

A third related study took place in a supermarket car park, where prominent stickers asked shoppers to return their carts to the main building. Keiser plastered various cars with the same flyer from the first study. If the garage was clear of carts, just 30% of shoppers littered with the flyer, but if four unreturned shopping carts were left lying about, 58% did so. Again, when people saw that one rule was broken, they felt less strongly about following another.

Together, these three experiments show that signs of disregarded rules can spread to affect commonly held behaviours (“don’t litter”) as well as specific requests from third parties (“don’t enter” or “return trolleys”).

Signs of disorder don’t even need to be seen to have such influences – they can be heard too. In the Netherlands, most people know that setting off fireworks in the weeks before New Year’s Eve is illegal and carries a small fine. Keiser found that he could trigger people to litter more frequently by giving them audible evidence that this law had been flouted. Again, he attached a flyer to bicycles parked near a train station. Under normal circumstances, 52% of cyclists littered but if they heard the sound of fireworks let off by Keiser at a nearby location, that figure grew to 80%.

For his final and most dramatic demonstration, Keiser showed that the mere presence of graffiti can even turn people into thieves. He wedged an envelope into the slot of a mailbox, with a 5 Euro note showing in the transparent window. If the mailbox and the ground around it were clean, just 13% of passers-by stole the envelope. If the mailbox was covered in graffiti, or if the ground around it was covered in litter, the proportion of thieves doubled to 27% and 25% respectively.

Keiser thinks that it’s unlikely that people inferred a reduced police presence by the presence of litter or graffiti – certainly, litter is generally tolerated by the police in Groningen. Instead, he thinks that one transgression was actually fostering another. This isn’t a simple case of imitation – littering doesn’t just beget littering. Keiser’s idea is that seeing the breakdown of one social norm makes it easier to ignore others, by weakening our general resolve to act appropriately and strengthening our temptations to act in our own self-interest.

All in all, the suite of experiments, all in a realistic setting, provide powerful evidence that the Broken Windows Theory is valid and all of Keiser’s results were statistically significant. Small, petty signs of disorder can indeed turn people away from the straight and narrow. His message to police and policy-makers is stark – it is worth spending time on small and seemingly trivial interventions, to prevent disorder from spreading and escalating.

My father is a detective for the local police department in my city, and he is literally a one-man graffiti unit; the only officer in the very large city (2006 census gave population as 709,893) who’s primary job is to investigate graffiti cases. I emailed him the link to this article even before I’d finished reading it; I’m sure this will be great information for him to have on hand the next time the city tries to cut his budget or reallocate his resources because it’s “just graffiti,” not a crime against persons. Oddly, that’s more or less what they said when they disbanded the property interdiction unit (read: investigation of burglaries and other kinds of property theft, and recovery of stolen property) that he used to be in. After all, who cares if victims never get their stuff back and the person who stole it is never brought to justice; not like the theif was “hurting” anyone, right? *eyeroll*

Interesting. I’m curious what the relative impacts of the sign and the graffiti are…. for example If we take a clean bike rack and no sign as our baseline. I would expect there to be less littering if there were a sign and no graffiti (because the converse of his argument would hold that seeing reinforced social norms should encourage you to follow other social norms). That there should be slightly more littering with graffiti and no sign, and even more littering with both graffiti and sign.
Also, this would seem to apply pretty broadly in some ways classical liberals might not like, for example drug policy. Under this model unenforced drug laws probably lead to higher instances of other crimes.

“I would expect there to be less littering if there were a sign and no graffiti (because the converse of his argument would hold that seeing reinforced social norms should encourage you to follow other social norms).”
Yes quite. And along a similar vein, would signs that affirmed positive social behaviour reduce the frequency of petty crime? Would the sight of, say, a community noticeboard or a full charity collection box make people less likely to steal or litter?
The thing I love about this study is it neatly tiptoes around the problem of confounding factors – you don’t need to account for socioeconomic or other differences between various areas if you’re looking at the same spot that you’ve experimentally altered.

Oh! The drug thing got me thinking. What is the effect of changing social norms? If there was a sign expressly allowing graffiti in a particular area, would that encourage it to be an ‘anything goes’ type area? Also, how long would the effect last? If there is nothing inherent about graffiti, then if it where to become the social norm, it should stop haveing an effect on other social norms… Or is graffiti an inherently selfish act that encourages other selfish acts such as not spending the time to throw something away or stealing… so many cool questions…

okay, last thing before I stop procrastinating….
A more direct test of the Broken Window idea would be to go to an area full of graffiti and clean up one area and see the effect it had. Then we would get an idea of how much would need to be done, and the magnitude of the effect it could have.

You might want to listen to the first 15 minutes of this BBC 4’s ‘Thinking Allowed’ of 22 October 2008. It is an interview with Robert J. Sampson, Professor of Social Sciences at Harvard University who delivered a lecture on Disparity and Diversity in the Contemporary City. Social Disorder Revisited. I found his argument convincing and interesting (and his results contradict the broken window theory).

Well, the first examples don’t show any connextion between graffiti and anything serious … I mean, come on, that graffiti is linked to litter doesn’t prove the broken window theory. The example with the bicicly had nothing to do with graffiti, it’s a common behaviour that you don’t repsect minor orders when you see others breaking them. Think of how people behave at a red light: When one of them starts going, most others will follow almost immediatly.
The situation with the letter is very special, since it’s in a house, where only few people have access – if that is graffiti covered, it says something about the vbery people who have access there. Someone who steals notices these things.
Buffing graffiti won’t keep anyone from beeing robbed, the broken window theory is a way for politics to produce visible results (less graff and litter) and link that with an improvement that’s harder to show (less crime).

Another anecdote–when my kids ( 3 and 6) come home, if the house is clean, they are much more likely to hang their coats up, and put their shoes away instead of throw the shoes and coat just anywhere. I think there is something going on here that is more than simple “cultural norms.” Hell, if the kitchen is already a mess, I am less likely to take the trouble to put my dishes away.

Maybe a good way to think about it is socially people will push the bounds of what they think is acceptable. It’s not that they think “littering is wrong” all the time, and just want to break that rule when they see a no graffiti rule broken; instead, it when a person sees one rule broken it’s some kind of challenge to their collected rules so they (subconsciously?) test the bounds of what may or may not be wrong.
Thoughts?

I think the most interesting aspect of the broken windows theory is that is reminds us that a “criminal” is not a different species from a “law-abiding citizen”. Most thieves would be upset if you lumped them in with violent muggers. Most murderers have some justification for what they’ve done, even if simply defending their honor, or doing something unpleasant that “had to be done”. People are people; we all respond to our social environment in similar ways. The way a generally law-abiding person responds to graffiti & litter (by moving a step towards lawlessness in response to the “trend”) should also apply to someone already further on the lawbreaker scale — move everyone over by one step, and you have a serious increase in crimes.
Obviously there are many more factors in crime than simply “what are other people doing”, and people in desperate situations will continue to do desperate & risky things, often illegal. But these factors are all important to understand, and the more they focus on people as PEOPLE and not separating the “criminals” from the “good guys”, the more success they will have.

Bikers who took the flyer home the first time will throw them away the second time. They don’t need two flyers. If Keiser would have used the graffiti the first time the results would have been the opposite.
In the second experiment, the first time bikers gave the new rules the benefit of the doubt. But after a while they noticed nothing was going on that was in need of the new rules so they were dismissed. Gradually the number changed from 27% to 82%, unrelated to bikes at the fence. Again, if Keiser would have started his experiment with bikes locked to the fence his results would have been the opposite.
There were no broken windows. Just people thinking for themselves and not behaving like the lab rats Keiser would like them to be. His experiments are a stunning fraude.

This is good. might help to motivate me to clean my house up more often!
I’ve often noticed that a building, even in a bad neighbourhood, can go for years without getting a broken window but as soon as one is broken, more will follow shortly afterwards. I’m assuming thats the broken window theory?
Also, of the industrial estates I work on, the ones that have the bigger budgets to keep them nice and clean are the ones that get less graffiti and fly tipping on.
Thanks, Ed! very interesting

At a more basic psychological level I wonder if the breakdown of social norms would be the same thing as needing to belong, i.e., people have a need to be a part of the group and fit into that group so the social norm defines how to fit into that group?

This is a very interesting subject! But my take on it is that this study is politically unusable. This study only stresses that the social environment in which individuals can be placed has an impact on their behaviour regarding social rules. But the fundamental point missed out for this study in order to have any sort of political impact would be a clear differentiation between actions included in social norms and actions that are outside these norms. In other terms, were those actions influencing people because they were outside of their social norms, or were they already by their inherent nature influencing them? An intercultural study would have yielded much more results. Even an historical view of the problem where specific behaviours frowned upon at one point would be completely integrate everyday life afterwards (or even sometimes a reversed situation, with a specific behaviour gaining a bad aura).
A lot of behaviour can thus be assessed, such as spitting, cursing, wearing certain type of clothes, driving habits, aso.
Intuitively, I would guess that it is mostly social norms that dictate the influence that can have certain behaviours. But as a skeptic, I would need evidence to back it up. Let’s hope that this sort of study is just the first step towards understanding social behaviours, and not a partial study that self satisfied politicians would use to back their biased ideology.

It shows that human behaviour is for a significant part influenced by the behaviour (and habits) of the community in the direct vicinity. If a local community doesn’t seem to care about litter so much, why would the person in question? Interesting also is the amount of people who don’t change their behaviour either way: the percentages of stable litterers and non-litterers.

Now that I think of it: In The Netherlands there is the saying: a good example makes a good following. What does this research add to things that every child can be taught by everyday life? It’s not really like a revelation you might say. But it’s nice to know that common knowledge is confirmed by scientific research

Well Kalief, you’ve got a prediction. Now you just need to go out and try to falsify it.
Personally I think the current results will stand, if people see that where rules were broken one week they are not the next, they might think the rules are being enforced, but it will be interesting to see if that bears out.

Good behaviour is equally infectious: visiting Disneyland in Orlando last year I noticed in first trip to the washroom that everyone – EVERYONE – washed their hands. Intrigued, our party of 5 spent the next 5 days looking for non-compliance and observed only one instance – a roughly 10-yr old child unaccompanied by parents. Otherwise handwashing was universal: men, women, even kids. We attributed this to the pervasive effect of Disney’s devotion to cleanliness at its theme parks.
Compare with the famously non-compliant behaviour of medical personnel in hospitals, something that has been studied repeatedly in recent years in Canada. Whereas the general public are observed to wash up better than 55% of the time, medical personnel average 43-45% in studies conducted in Toronto & Montreal teaching hospitals. Doctors average less than 35% (surgeons worst at 25%), nurses ~45%, only technicians do better than 50% (radiologists best at ~55%).
Combine this with personal observations of local hospitals that have cut back on housekeeping expenses (and consequently cleanliness) to reduce operating costs. In particular, I’ve noted washrooms universally lacking supplies of soap &/or paper towels, and even the waterless handcleaner stations (ubiquitous now post-SAARS epidemic experience) generally lacking liquid, even at a teaching hospital that lost both patients & staff to SAARS (North York General in Toronto, if you’re listening).
Repeated appeals by authorities & press to medical personnel to wash hands have been unsuccessful in changing behaviour. I wonder whether a Disney approach to cleanliness – zero tolerance in housekeeping – wouldn’t influence people better than reports in medical journals & newspapers & regular, if futile, memos from health authorities.
Can anyone report on whether such an approach has been tried and whether it did in fact change staff behaviour?